Fig. 1 The framework showing the different mechanisms of ecological resilience of pollination in the face of pollinator decline. The global changes, such as land use change, invoke the variations in pollinator community. Under the mechanisms of ①functional redundancy, ②density compensation, ③response diversity, ④interaction turnover; ⑤cross-scale resilience, pollinator communities are able to deliver an acceptable level of pollination functioning (e.g. pollen grains on stigma surface), forming the ecological resilience of pollination.

Fig. 2 Conceptual diagram showing the mechanical effect of functional redundancy among functional groups of pollinators on ecological resilience of pollination. Three functional groups (a, b and c) are supposed to pollinate the flowering plants in the ecosystems (A). When the amount of pollens delivered by functional group a (yellow) and functional group c (orange) decreases, the amount of pollens delivered by functional group b (blue) increases (B). The number of pollens deposited on stigma surfaces does not change. The pollinator communities have the ecological resilience of pollination.

Fig. 3 Conceptual diagram illustrating the mechanical effect of density compensation on ecological resilience of pollination. Two functional groups of pollinators (a and b) are supposed to deliver pollens on stigma surfaces (A). In the face of global changes, the pollinator communities with 4 individuals of functional group a and 5 individuals of functional group b (A) is transformed to a different pollinator communities with 2 individuals of functional group a and 9 individuals of functional group b (B). The visit density of functional group a decreases, but the visit density of functional group b increase, and vice versa (B). Due to the differences in pollination efficiency (e.g. pollen deposition per visit), the overall pollen numbers delivered by different pollinator communities are the same. The pollinator communities have the ecological resilience of pollination.

Fig. 4 Conceptual diagram showing the mechanical effect of response diversity on ecological resilience of pollination. Pollinators are supposed to be different in body size and nesting site. The pollinators with different body sizes (A) respond to natural habitats at different spatial scales, with a relatively large scale of effect for the large pollinators compared to a relatively small scale of effect for the smaller pollinators (B). Meanwhile, the pollinators with different nesting sites (C) respond differently to the natural habitats, with a decrease of populations for most pollinators along the loss of semi-natural habitats but an increase or stability of populations for other pollinators (D). Response diversity can affect ecosystem pollination functioning through effect diversity. The overall pollen numbers delivered by pollinators keep the same. The pollinator communities have the ecological resilience of pollination (E).

Fig. 5 Conceptual diagram illustrating the mechanical effect of interaction turnover on ecological resilience of pollination. The ecosystem is hypothesized to have an original pollination network with three pollinators (a1, a2, a3) and three plants (p1, p2, p3) (A). Under disturbances, some interactions are lost but new interactions occur, forming interaction rewiring (B). Interactions are also lost as a result of pollinators decline, but new interactions is built as new pollinators (a4) enter the pollination network, resulting from species turnover of pollinators (C). The combined effect of interaction rewiring and species turnover explains an interaction turnover of the pollination network (D). For plants, their pollinator assemblages are different before and after interaction turnover, however, the amount of pollens delivered by the pollinator assemblages is the same. The pollinator communities have the ecological resilience of pollination (E). Black lines indicate the original interactions before interaction turnover and red lines indicate newly-built interactions after interaction turnover.

Fig. 6 Conceptual diagram showing the mechanical effect of cross-scale resilience on ecological resilience of pollination. The ecosystems are hypothesized to have three functional groups with large (1,500 m), medium (1,000 m) and small (300 m) spatial scales (i.e., foraging ranges), respectively, and they pollinate flowering plants a, b, c, d, e and f spatially distributed in ecosystems. The large-sized functional groups pollinate plants across scale (A). The three functional groups of pollinators are distributed discontinuously along the x-axis of body size (B). Flowering plant a is pollinated by three functional groups, flowering plant b, d and f are pollinated by two functional groups, and flowering plant c and e are pollinated by just one functional groups. Therefore, the level of cross-scale redundancy of pollinator assemblages for plant a is higher than that of other plants (C). If the visit density of a certain functional group of pollinators with a specific foraging range (e.g. 300 m) declines (e.g. plant a), other functional groups of pollinators with a large spatial foraging range (e.g. 1,500 m) increase their visit densities. The amount of pollens delivered by the pollinator assemblages on the stigma surface of plant a is similar. The pollinator communities have the ecological resilience of pollination (D). In (C) and (D), the lengths of lines corresponding to the pollinators indicate the foraging ranges of pollinators and the widths of lines quantify their pollination functioning.